Conventionally, light emitting diode (LED) is widely utilized as an illumination light source. In comparison with an incandescent lamp or a fluorescent tube, the LED includes a characteristic that the response speed is high. A visible light communication technology is investigated which makes use of the characteristic to cause the LED to flicker at a rate at which the flickering may not be recognized by the eyes of the human being thereby to superpose information (which may be referred to as signal) on the illumination light to be emitted from the LED to perform communication. The visible light communication technology is examined such that it is, for example, utilized for communication applications at a place at which use of radio waves is restricted, information transmission where information transmission is restricted to a range within which light may reach such as the inside of a room, intelligent transport systems (ITS) or the like.
For example, Japanese Laid-open Patent Publication No. 03-10483 discloses a certain one information transmission system that includes a light emission unit whose given region is caused to emit light to transmit information and a light reception unit for decoding information from images obtained by imaging the given region in a time series. The information transmission system discloses that the light emission unit emits light color-modulated by performing multi-leveling to at least three values in response to information of the given region and the light reception unit decodes the information on the basis of the multi-leveled color modulation information of the given region.
Further, for example, International Publication No. WO 2009/136312 discloses a technology that a certain one optical module includes at least two primary light sources for emitting primary color light and data is incorporated into light by modulating a color coordinate of light to be emitted from the primary light sources in response to data to be embedded. Since the sensitivity of the eyes of the human being to a color in variation of the color is lower than that in variation of the intensity, where the optical module described above is utilized for an illumination system, data may be embedded into light to be emitted without degrading the function for illumination.